"We discussed it. You know the same thing we talked about, the need for transparency, full and complete investigation,” Mattis told a small group of reporters traveling with him, referring to a meeting with the Saudi official on Saturday, the news service reported.

“[There was] full agreement from foreign minister al-Jubeir, no reservations at all, he said we need to know what happened and it was very collaborative, in agreement,” he added.

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At the conference Saturday, Mattis said that Khashoggi's killing undermined regional stability and promised that the U.S. would take additional measures to punish those responsible.

“With our collective interests in peace and unwavering respect for human rights in mind, the murder of Jamal Khashoggi in a diplomatic facility must concern us all greatly,” Mattis said.

Khashoggi disappeared on Oct. 2 after entering the Saudi consulate in Istanbul.

Turkish authorities have said he was tortured, murdered and dismembered by Saudi operatives.

Saudi Arabia has denied Turkey's narrative with shifting explanations. The kingdom first asserted Khashoggi left the building alive the day he disappeared and later announced that an initial investigation found he had died in a brawl.

The U.S. has begun to punish Saudi Arabia and Trump has promised to deal severely with those culpable.

Trump has voiced hesitancy to rupture diplomatic ties to the kingdom, which the U.S. is backing in a proxy war with Iran in Yemen and which is allied with the U.S. against Iran, Russia, Turkey and Syrian President Bashar Assad.